Brownian motion in superfluid $^4$He

Xiao Li, Ran Cheng, Tongcang Li, Qian Niu

Published 2011-07-03, updated 2011-07-26Version 2

We propose to study the Brownian motion of a classical microsphere submerged in superfluid $^4$He using the recent laser technology as a direct investigation of the thermal fluctuations of quasiparticles in the quantum fluid. By calculating the temperature dependence of both the friction coefficient and the strength of the random force, we show that the resonant mode of the fluctuational motion can be fully resolved by the present technology. Contrary to the previous work, it is found that the roton contribution is not negligible, and it even becomes dominant when the temperature is above 0.76\,K.